1. Field of the Invention
The present invention relates generally to ophthalmic lenses and more specifically to intraocular lenses having an extended depth of focus.
2. Background
Intraocular lenses (IOLs) are commonly used to replace the natural lens of the eye under cataract conditions. Alternatively, the natural lens may be replaced to correct other visual conditions, for example, to provide accommodation or pseudo-accommodation in the event a subject develops presbyopia and has diminished focusing capability on both distant objects and near objects. “Accommodation” is the ability of the eye to change focus from near to far, far to near, and all distances in between. As presbyopia progresses, accommodation ability generally decreases. For example, with presbyopia, which usually begins at around age 40, the lens becomes less flexible. As the ciliary muscle contracts to move the lens forward, the lens typically resists due to presbyopia. Accommodating and/or multifocal intraocular lenses may be used to restore at least some degree of accommodative or pseudo-accommodative ability.
Accommodating intraocular lenses (AIOLs) are generally configured to focus on objects over a range of distances typically by moving axially and/or by changing shape in response to an ocular force produced by the ciliary muscle, zonules, and/or capsular bag of the eye. Current accommodating intraocular lenses are capable of providing about 0.5 diopter of objective accommodation. Multifocal intraocular lenses (MFIOLs) provide a pseudo-accommodation by simultaneously providing two or more foci, for example, one to provide distant vision and the other to provide near vision. This pseudo-accommodation may have some trade-off, such as dysphotopsia (e.g., halos or glare), reduced contrast sensitivity due to the continual presence of defocused light, reduced intermediate vision, pupil dependent performance, or the like. Over time, patients with multifocal intraocular lenses generally select the focus that provides the sharper image and ignore other blurred images.
Another approach to providing some degree of simulated accommodation is by extending the depth of focus of a traditional monofocal lens so that objects over a broader range of distances are simultaneously resolved. This approach also has some trade-off with reduced contrast sensitivity. Examples of this approach are discussed in U.S. Pat. Nos. 6,126,286, 6,923,539, and 7,061,692.
An intraocular lens is needed that extends the depth of focus of an eye while minimizing the occurrence of one or more factors reducing the optical performance of the eye, such as dysphotopsia, reduced contrast sensitivity, reduced intermediate vision, pupil dependent performance, or the like. More particularly, an intraocular lens is needed that extends the depth of focus of an eye without significantly reducing the in-focus visual acuity of the eye and while minimizing the occurrence of one or more factors reducing the optical performance of the eye, such as dysphotopsia, reduced contrast sensitivity, reduced intermediate vision, pupil dependent performance, or the like. Further, systems and methods for extending the depth of focus of the eye while minimizing the occurrence of one or more factors reducing the optical performance of the eye are needed.